1. Field of the Invention
This invention relates to semiconductor processing and, more particularly, to a method, system, and storage medium for gas flow calibration of mass flow controllers.
2. Description of the Relevant Art
Many process tools used in semiconductor fabrication require regulated flow of various gases into the process tool. Mass flow controllers ("MFCs") are ubiquitous in semiconductor fabrication for regulating the flow of gases into process tools. Each process tool typically has a gas tray which includes a MFC for each gas used by the process tool. Accurate processing often requires that the gas flow be carefully regulated. Failure to accurately control the gas flow may result in the fabrication of defective integrated circuits. To ensure accurate gas flow requires that the calibration of each MFC be checked on a regular basis. For example, the calibration may be checked as often as once every two weeks.
MFCs are often calibrated using mass flow meters (MFMs). The MFMs may be located in an external test rig which can be attached to the gas tray to calibrate the MFCs or, preferably, the MFMs may be located on the gas tray thereby allowing more frequent checks on the MFC calibrations. MFMs are typically only accurate between 5% and 95% of their full scale readings. Process tools, however, often require flow rates of different gases that differ by two or more orders of magnitudes. For example, process tools may have MFCs with full scale ranges of 20 slm and 200 sccm on the same gas tray. To calibrate a 20 slm MFC typically requires a 20 slm MFM, however, a 200 sccm MFC has a full scale range that is only 1% of the full scale range of the 20 slm MFM and, therefore, the 200 sccm can not be calibrated accurately using the 20 slm MFM directly. To calibrate both a 20 slm MFC and a 200 sccm MFC on the same gas tray requires the gas tray contain multiple MFMs. Having multiple MFMs on a gas tray increases the complexity and cost of the gas tray.
It is therefore desired to have a gas tray that requires only a single MFM on the gas tray to calibrate MFCs that have vastly different flow rates. It is also desired that the calibration be easy to perform quickly thereby allowing the calibration to performed more frequently.